He pointed proudly to the French drain and the large sump pump in my storage unit, admitting that water would find its way through the porous walls. We shrugged, resigned to the dampness that would never allow us to store much down there.
It was the first summer, in , that we realized we had a problem. The sheets of plywood the builders had used to build our three storage units were covered in dark greenish fuzz.
We got the plywood out of there, sprayed everything we could with vinegar, and eventually tried a dehumidifier. After research and condo meetings, we went back to opening the windows, with the theory that air circulation was important.
Somehow we made it through without many issues, thought the basement remained damp and musty. Life went on: the neighbors on the first floor had twins, Tom and I got married and agreed to stay in our city condo. Uh oh. Tom and I returned from Vermont to see what the hot, humid weather had wrought on our basement. It was bad. Really bad. Those latent spores had exploded — covering every surface with a nasty fuzz.
The ceiling joists, the dirt floor itself, every bit of wood, plastic or metal where city soot had floated in the windows, providing a food source for our microbial guests. While this sounds like a good move, it leads to condensation. Walls and windows start sweating. Think of what happens when you remove a water bottle from the fridge in hot weather. Water droplets form on the outside because the outside air contains more moisture.
The same thing happens when moisture-laden air from the outside floats into your cool basement. Condensation is a major problem in summer. It will instigate wood rot, encourage pests, cause wood to warp, and make your HVAC work harder. Add to it the inconveniences of repairing your moisture-damaged interior. Imagine taking a cold beverage outside on a hot summer day; the drink container will sweat, which is condensation. The same thing is happening when basement windows are opened.
When the warm, humid outside air comes into the basement and comes into contact with the cool basement surfaces, it will form condensation. Condensation is wet, which makes your basement wet, which is the perfect place for musty, smelly, mold.
Finishing a basement without first dealing with the moisture problems can result in making health conditions worse and lead to significant damage as well.
Basement water problems are solvable, but there is a cost to doing it right. To correct basement moisture problems, it's necessary to understand where the water is coming from and what mechanisms permit it to enter the basement. There are just three sources of moisture:. Moisture is transferred from the outside of the building to the basement interior by four mechanisms:. Sometimes problems are traced to poor construction with cracking, settling foundations. In many cases, however, houses and basements can be structurally sound but are often not properly built to handle water drainage.
Failure to slope the ground surface away from the foundation or lack of a good gutter and downspout system is common. Missing or nonfunctioning subsurface drainage systems are also found relatively frequently.
These problems can all be addressed and corrected if a systematic approach is used. In a 1-inch rain, 1, gallons of water fall on the roof of a 2,square-foot house. Without proper grading, gutters and downspouts, some of this water flows into the basement. The below-grade water table can also rise due to flooding or seasonal site conditions. This is why drain tile systems are recommended around basement walls even in sandy or gravel soils.
Moisture is generated inside of basements from people and their activities. Common sources are humidifiers, unvented clothes dryers, showering and cooking. When basements are finished, these activities increase.
Another source that can be thought of as internal is the moisture contained in new concrete after construction. In a typical house, this can amount to 0. It may take many months or even years for a new house to come into equilibrium with its environment. In the summertime, basement windows may be opened for fresh air. If the outside air is warm and humid, it will condense on the cool basement wall and floor surfaces.
Many homeowners see this moisture and believe they are experiencing basement wall leakage, when in fact the accumulated moisture is from condensation. Capillary suction moves moisture through porous materials. The water can be drawn upward through small pores in the concrete footing and slab and laterally through walls. This effect creates the ring of dampness seen at the base of many basement walls. This is very common at cold joints. Water can rise by capillary draw significantly as shown below:.
In most houses, a stack effect is created because warm air rises. This induces a negative pressure on the basement and draws moist air in through any cracks or openings in the foundation including open sump pits.
For this reason, sumps should have an airtight cover. With a concrete block foundation, moist air is drawn through the block cores, especially if they are left open at the top course. Vapor diffusion is the movement of moisture in the vapor state through a material. It's dependent on the permeability of the material and the driving force of vapor pressure differential.
In a basement, vapor can diffuse from the wetter ground through concrete walls and floors toward the dryer basement interior. Vapor retarders such as foundation waterproofing and polyethylene slow down this process.
The soil next to the house is often backfilled without proper compaction and later settles. This is especially true under stoops where water can collect next to the basement wall.
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